120,476 research outputs found
Cowpox virus infection in natural field vole Microtus agrestispopulations: significant negative impacts on survival
No full text1. Cowpox virus is an endemic virus circulating in populations of wild rodents. It has been implicated as a potential cause of population cycles in field voles Microtus agrestis L., in Britain, owing to a delayed density-dependent pattern in prevalence, but its impact on field vole demographic parameters is unknown. This study tests the hypothesis that wild field voles infected with cowpox virus have a lower probability of survival than uninfected individuals. 2. The effect of cowpox virus infection on the probability of an individual surviving to the next month was investigated using longitudinal data collected over 2 years from four grassland sites in Kielder Forest, UK. This effect was also investigated at the population level, by examining whether infection prevalence explained temporal variation in survival rates, once other factors influencing survival had been controlled for. 3. Individuals with a probability of infection, P(I), of 1 at a time when base survival rate was at median levels had a 22.4% lower estimated probability of survival than uninfected individuals, whereas those with a P(I) of 0.5 had a 10.4% lower survival. 4. At the population level, survival rates also decreased with increasing cowpox prevalence, with lower survival rates in months of higher cowpox prevalence. 5. Simple matrix projection models with 28 day time steps and two stages, with 71% of voles experiencing cowpox infection in their second month of life (the average observed seroprevalence at the end of the breeding season) predict a reduction in 28-day population growth rate during the breeding season from λ = 1.62 to 1.53 for populations with no cowpox infection compared with infected populations. 6. This negative correlation between cowpox virus infection and field vole survival, with its potentially significant effect on population growth rate, is the first for an endemic pathogen in a cyclic population of wild rodents
Magnetic field enhancement by cross-field diffusive flow
No full textPlasma transport by diffusion across magnetic field lines is proposed as a mechanism for magnetic field enhancement. It is shown that anomalous plasma diffusion can induce a substantial amount of magnetic flux under certain circumstances. Application to magnetic field enhancement in sun-spots and some laboratory devices is discussed, and an experiment for testing the mechanism is proposed.X117sciescopu
Magnetic field induction by Bohm plasma diffusion
No full textWhen Bohm diffusion is incorporated, the magnetic induction equation can be transformed into a type of heat equation which allows exact analytical solutions ( Lee and Ryu 2004 Phys. Plasmas 11 5462). This equation can admit amplification solutions for the axisymmetric magnetic field, if the diffusion velocity satisfies a certain condition. This paper discusses the case of the azimuthal field and finds that there are also analytical solutions which can amplify the magnetic field.X11sciescopu
Amplification of axially symmetric magnetic field by Bohm particle diffusion
No full textThe magnetic induction equation for an axially symmetric magnetic field reveals an interesting feature, when the Bohm plasma diffusion is incorporated. The 1/B dependence of Bohm diffusion allows the induction equation to transform into a simple heat equation which admits an exact solution when the plasma temperature is constant. When the diffusion velocity satisfies a certain condition, the axially symmetric magnetic field can be significantly enhanced. (C) 2004 American Institute of Physics.open1110sciescopu
Preferential acceleration and magnetic field enhancement in plasmas with e+/e- beam injection
No full textA theoretical model of current filaments predicting preferential acceleration/deceleration and magnetic field enhancement in a plasma with e(+)/e(-) beam injection is presented. When the e(+)/e(-) beams are injected into a plasma, current filaments are formed. The beam particles are accelerated or decelerated depending on the types of current filaments in which they are trapped. It is found that in the electron/ion ambient plasma, the e(+) beam particles are preferentially accelerated, while the e(-) beam particles are preferentially decelerated. The preferential particle acceleration/deceleration is absent when the ambient plasma is the e(+)/e(-) plasma. We also find that the particle momentum decrease can explain the magnetic field increase during the development of Weibel/filamentation instability. Supporting simulation results of particle acceleration/deceleration and magnetic field enhancement are presented. Our findings can be applied to a wide range of astrophysical plasmas with the e(+)/e(-) beam injection. (C) 2016 AIP Publishing LLC.110sciescopu
Electron acceleration by a circularly polarized laser pulse in the presence of an obliquely incident magnetic field in vacuum
No full textLaser-induced acceleration of an electron injected initially at an angle to the direction of a circularly polarized laser pulse in the presence of an obliquely incident magnetic field has been investigated. For a suitable position of the peak of the laser pulse, the external magnetic field exists at an angle such that it can be parallel to the magnetic field of the laser pulse. The electron gains considerable energy and retains it even after passing of the laser pulse in the presence of an optimum magnetic field in vacuum. The electron attains the maximum amount of energy at a particular angle of the incident magnetic field due to the betatron resonance. (c) 2005 American Institute of Physics.open113528sciescopu
A nehézségi erőtér regionális szerkezetének kutatása új típusú földi és szatellita mérések bevonásával = Regional gravity field research by using new kinds of terrestrial and satellite measurements
No full textA vizsgálatainkat a magyarországi geoidmeghatározás, a geoidfelület interpoláció, továbbá a GOCE gradiométeres műhold jövőbeni méréseinek felhasználása főbb területein végeztük. Elvégeztük a kombinált geoidmegoldáshoz felhasználható adatok gyűjtését és rendszerezését, adatbázisba vitelét és az adatok vizsgálatát. Megfelelő számítási eljárásokat dolgoztunk ki az adatok integrált felhasználása céljából, különös tekintettel a GOCE méréseire. A projekt fő eredményeként egy új, HGTUB2007 jelű geoidmegoldást készítettünk el Magyarország területére geopotenciál modell, gravimetriai, GPS/szintezési, függővonal elhajlási, Eötvös-inga és DTM adatok kombinálásával. A végső megoldásban gyakorlati okokból nagy súllyal szerepeltek az Országos GPS Hálózat (OGPSH) 95 szintezett pontjának mérései. A számított geoidmegoldás az OGPSH kiválasztott pontjaira az elvégzett összehasonlítások szerint 2 cm-es szórással és 6 cm-es maximális eltéréssel illeszkedik. Az illeszkedés azért fontos, mert a geoid magyarországi felületdarabja pontos ismeretének kulcsszerepe van a gyakorlati életben a GPS-szel történő magasságmeghatározásban. Ez a meghatározás világviszonylatban is egyedülálló, mivel ilyen jellegű az adatokat, és különösen az Eötvös-inga mérési adatokat most első alkalommal sikerült az egész ország területére egy egységes feldolgozási folyamat keretében összekapcsolni a még pontosabb regionális erőtér modellezés céljából. | Our research was carried out in the main fields of gravity field determination for Hungary, interpolation of the geoid surface and application of gradiometric data of the future GOCE satellite mission. First the task of gravity data collection, data management and testing was done with the intention to carry out a new combination geoid solution. Suitable methods were developed for integrated data processing especially considering GOCE measurements. The main output of the project is a new Hungarian geoid solution HGTUB2007, achieved by combining geopotential, gravimetric, GPS/levelling, vertical deflection, torsion balance and DTM data. For practical reasons th 95 GPS/levelling data of the Hungarian GPS Network (OGPSH) have been assigned large weights. Our tests showed a fit of 2 cm in terms of standard deviation and 6 cm maximum deviation for selected OGPSH points. This is important in practice, since accurate knowledge of the geoid surface is the key to GPS heighting. This determination is unique in several respects, since by now no geoid solution has been achieved, especially for which surface gravity gradients have successfully been combined with other gravity field quantities for accurate regional gravity field determination
OCCCA Presents Tom Field
No full text43 x 28 cm.Promotional broadside adertising a showing of the works of painter Tom Field June, 2001. Contains painting by Tom Field. 43 x 28 cm
Multi-anyons in the magnetic field
No full textWe consider the external magnetic field effects on the two types of anyons with fractional statistical parameter pig with coprimes p and q, one with a fractional charge e/q and the other with a fractional flux p phi(o)/q by exact ground state wave function. We also study the geometry in which a two-dimensional strip of anyons contains an island of anyons with different statistical parameters in their equilibrium. The equilibrium inside an island is shown to be periodic with respect to the magnetic flux through the island. The period for the fractional charge anyon equals to the integer multiple of the fundamental flux quantum. On the other hand, in the case of the fractional flux anyon, the period is found to be the fractional multiple of the fundamental flux quantum.X11sciescopu
Selection of an electron path of high-order harmonic generation in a two-colour femtosecond laser field
No full textWe theoretically investigate the process of high-order harmonic generation ( HHG) in an intense two-colour femtosecond laser field, of which both fundamental field and its second harmonic are linearly polarized. With the second harmonic field added, new degrees of freedom become available for controlling the process-relative phase between the two components and angle between the two polarization axes. It is shown that these parameters can be adjusted so as to select an electron path contributing to the process, leading to HHG from either a short path or a long path. As a result of this selectivity, regular and strong attosecond pulses can be generated.This research was supported by the Korea Science and Engineering Foundation (KOSEF)
through the Creative Research Initiative Program
- …
